Olfactory impairment in mild cognitive impairment with Lewy bodies and Alzheimer’s disease

Abstract

Objectives: Impaired olfaction may be a biomarker for early Lewy body disease but its value in Mild Cognitive Impairment with Lewy bodies (MCI-LB) is unknown. We compared olfaction in MCI-LB with MCI due to Alzheimer’s disease (MCI-AD) and healthy older adults. We hypothesised that olfactory function would be worse in probable MCI-LB than in both MCI- AD and healthy comparison subjects (HC). Design: Cross-sectional study assessing olfaction using Sniffin’ Sticks 16 (SS-16) in MCI-LB, MCI- AD and HC with longitudinal follow-up. Differences were adjusted for age and receiver operating characteristic curves were used for discriminating MCI-LB from MCI-AD andHC. Setting: Participants were recruited from Memory Services in the North East of England Participants: 38 probable MCI-LB, 33 MCI-AD, 19 possible MCI-LB and 32HC. Measurements: Olfaction was assessed using SS-16 and a questionnaire. Results: Participants with probable MCI-LB had worse olfaction than both MCI-AD (Age-adjusted mean difference (B)=2.05,95% CI:0.62-3.49, p=.005) and HC (B=3.96, 95% CI:2.51–5.40, p<.001). The previously-identified cut-off score for the SS-16 of ≤ 10 had 84% sensitivity for probable MCI-LB (95% CI: 69-94%) but 30% specificity vs MCI-AD. ROC analysis found a lower cut-off of ≤ 7 was better (63% sensitivity for MCI-LB, with 73% specificity vs MCI-AD and 97% vsHC). Asking about olfactory impairments was not useful in identifying them. Conclusions: MCI-LB had worse olfaction than MCI-AD and normal ageing. A lower cut-off score of ≤ 7 is required when using SS-16 in such patients. Olfactory testing may have value in identifying early LB disease in memory services.